Radio receiver



July 16, 1946.

HARRY WHALLEY CHARLES WALTER MILLER ATT ORNEYS Patented July 16, 1946RADIO REoEIvER Harry Whalley, Darwen, and CharlesV Walter ,Millen Sale,England, assignors .to Metropolitan-Vickers Electrical Company Limited,London, England, a company of `Great Britain Application December 16,1943, Serial No.

l In England August 8, 1941.

1 claim. (c1. 25o-20) t This invention relates specifically toso-cv'alled f with. thefrequency 'of .the persistence, of vision, the

output or outputs due to any received radio transmissionsA whichmay-v betaking place within the waveband being indicated as resonance or peakcomponents perpendicular to atime base waveband component on the screenof a cathode ray tube the time base component being providedsynchronously with the scanning such as by means of a saw-toothtype ofoscillation generator. Provision can-be madewhereby any selected one ofthe `,thus indicated transmissions can be tuned into manually and itsmodulation listened to or recorded or` otherwise indicated, that is tosay, the scanningr of the waveband can be effected solely by hand suchas through the turning .of a knob about an associateddial indicating thewavelength. In such a panoramic receiver it has been convenient for thepurpose of therapidscanning oithe waveband tofffwobble the'value ofcertain ltuning components -of the oscillatorsection.

of, vafrequency changer valve in -a superheteros vdynecircuitwhichsuperheterodyne circuit preferably4 has 4three stages of `frequencychanging withcorresponding intermediate frequency circuitsi land,preferably 5 the ,scanning is `effected by aireactor valveassociatedwith the second ofthe oscillators through'lan amplifier as described inUnitldStates application Serial No. 503,277, -led September, 21; 1943- Ywhat heejee .Celledthe Single-Span, tuning principle in domestic andotherfradio receivers has been proposed but has not apparently come intocominercialuse. y

The generaladvantages offthesuperheterodyne receiver over other typesare also well known and its use in a panoramic receiver is highlydesirable, and when panoramic receivers are required to scan arelativelyvlarge number of wavebands, for instance twenty or thirty,there may be great complexity and expense unless provision is made forreducing the number of preset tuning circuits which have to be changedwhen the waveband to be scanned is altered. In order that the receivedsignals shall have sufficient amplitude at the first frequency changerto override valve noise in the mixer some signal frequency amplificationis generally desirable. It is, however, also desirable kthat image"frequency signals fare removed as far as possible from the wavebandscovered by the receiver.

The invention is based on the above considerations which are given ingreater detail in the following statement which includes furtherconsiderations.

In general a satisfactory panoramic receiver shouldhave a highsensitivity to enablethe maximum number of signals to be observed, b theselectivity should be high to give adequate disn crimination betweenadjacent signals, consistent with thetuned circuits being kable torespond at the rate of time base sweep and of scanning synchronouslytherewith, cit is desirable at thesame time thatsecond channelinterferenceshould be absent or substantially absent; d the process ofscanning should involve the smallest numberoi tuning parameters aspossible; and e tuning can be conveniently carried out byelectronicrather than mechanical means. Y Regarding a above, thisinvolves high overall gainjwhich isconveniently obtainable by the use ofan ,amplier of standard design operated at,

for example, 1.6 Irnc. per second or 465 kc. pe-r second. VThis willalso satisfy requirement b above while the consequent use of asuperheterodyne circuit simplies the requirement d above but itintroduces the difficulty of second. channel interference c above'. Asan example, a particular receiver may be quoted which was required tocover afrequency range of fromfifteen to thirty megacyclesper second inthirty consecutive bandseach of five hundred kilocycles per secondwidth;such receiver therefore had to be capable of tuning automaticallythrough five hundred kilocycles per second on each of the bands at arecurrence freguency of the order ofrtwenty-iive per second. To

"achieve this mechanically with normal input circuits Wouid hayeinvolved the use of at least two.-

continuously variable timingdevices such as automatically rotatingcondensers, as wellgascomplicated band switching means to cover thenecessary number of bands. effected electronically such as by means of areactor valve, the switching would not be simplified; therefore apreliminary frequency changing stage (it is preceded by asignalfrequency ampli-v er) was proposed for converting allsignals to afrequency band of ve hundred kilocycles persecond in Width vso that asingle automatically variable oscillator and its associated frequencychanger would suflice to produce the panoramic sweeps, irrespective ofthe band to which the receiver was adjusted.

According to the present invention a panoramic If the tuning Were to bef receiver has at least two and preferably three whilst the firstoscillator frequency is high for giving a first intermediate frequencyhigher than 5 any signal 'frequencyr so that the-"tuned Ycircuitvelements, preferably condensers only, which have to be selectivelyswitched to the fixed element of the receiver for frequency bandchanging are reduced, namely tothose of the oscillator circuit lY whichresponds uniformly over the band, in the example 33 .mc.i250 kc./sec.and attenuates outside it.- M. 2l is the second mixer stage suppliedjbecause the image frequency is so high/that it can easily be filteredout, or is even inherently eliminated. The aperiodic signal frequencyamplifier 4 .j does not increase the selectivity and gives only aY smallgain, but it has beenfound in the coml5 bination above set forth toVgive satisfactory per-- formance in practice and also, duetojits'inability to deal with such high frequencieahelpSJlo. iilteroutthe image frequencies. The first inter-` mediate frequency amplifiercircuit` preferably has a' band-pass characteri'sticrcfv adequateifrequency width which may be, for example,' five hundred kilocycles persecond'so' that the frequency wobbling can be done' at the second os`cillator, thus enabling all bands Vselected to have an equal Width. i

In an example olf panoramic receiverinaccordance withV the invention fora signal Vfre` quency rangeof fifteen' to thirty megacycles in steps offive hundred kilocycles-per second, the

. first oscillator frequency is `from forty-eight to circuits arepermissible and yet second 'channel interference is avoided, Whilst thechoice of band to be observed is decided'fmerely by the tuning of thefirst oscillator. The use of )this arrange` ment in conjunction withamain'intermediate 45 Y frequency amplifierV with V its .frequencies ichosen appropriately, enables'adequate selectivity, sensi` tivity andfreedom from second channel inter-` ference to be obtained,-inspite of.fthe simple nature of the input circuits and the necessarily widefrequency band passed Yby the fr'stintermediate frequency amplifier.' Itis to be under` Vst'oo'd'that wev do' notherein claim per seautomatically varying the tuning of the second osY cillator instead ofthe first, in a panoramic re'-` 55 ceiver, f

' The :accompanying drawing is a block diagramLA indicating a particularpanoramic radio receivern in accordance with the presentinvention." f

Starting from the left-hand end of the'diagram 60 the rectangle A. l2..F. AL represents the desirable 2,404,333 1 ,i :ff ifi;

radio frequency amplifier stage which is aperi-V band of signalsbeingscanned. y #It' that the scanning is over a band of one-,half'megacycle I. F. A, I is the first intermediate frequency amplifier,which may include a filter from I,- F. A; l Aand from the secondoscillator 0.2

the frequency of which, in the example, is lWob- Y Y bled betweenthelimits of 34.35 and 34.85 mc./ .'isec. L F. A. 2 is the secondintermediate frequency amplifier, sharply tuned to 1.6 mc./sec. M. 3is'the third mixer stage, supplied from I. F. A. 2 and from the thirdoscillator 0.3, the frequency of which is 2.065 mc./sec. The mixer M.' 3feeds to they third intermediate .frequency amplifier I. F. A. 3 tunedto 465 kc./sec., this amplifier feeding to the detector Dwhich ispreferably associated with a limiter L in accordance with UnitedV StatesApplication Serial No.' l503,280,7iiled .September- 21, 1943.1y TherectangleB. F. O. Vrepresents the beat frequency oscillatorfwhich may beused for heterodyning a continuous wave signal;

in order to obtain an audible beatnote if desired The output from theVdetector goes, on the one hand, to the audio frequency amplifier A. A.su

plying the phones VVlh. or loud speaker or other fed from the timeY basegenerator represented by In a panoramic receiver, an inputradiofrequency amplierstage-aperiodic over the 'range f Aof signals tobe received, a first frequency changer stage variable to select a bandof frequencies of substantiallyA constant' Width to bescanned p andarranged to convert the selected band to an ine termediatefrequency-higher than that ofthe re'v ceived signal, an intermediate frequencyampli fier, a second frequency changer'stage for 'scan-A ning the bandselectedv byY the'rst frequency changer stage', means for varying theoscillator frequency of said secpndfrequency changer stage to Veffectpanoramic scanning,` and adetector stage forthescannedsignalsl'r j;

HARRY

